Process for the manufacture of cellulose acetate



Patent ed Jan. 10, 1928 umTEos AT s PATENT OFFICE.

EONARD ANGELO LEVY, or LONDON, ENGLAND.

rRocEss Eon THE MANUFACTURE or CELLULOSE ACETATE.

No Drawing. Application filed April- 4, 1925, Serial No. 20,866, and in Great Britain April 9, 1924.

My invention relates to an improved process for the manufacture of cellulose acetate by the treatment of cellulose-or modified cellulose with an acetylating mixture consisting '6 of acetic anhydi'ide, acetic acid and a condensing agent, such as sulphuric acid.

Now, I have found by experiment. that by the addition to the acetylating mixture of a metallic catalyst consisting of a salt of chromium, the acetylation process. is considerably promoted and the acetone soluble product as finally obtained is in a very favorable form with regard to clarity of solution and condition of the finished acetate in a relatively short space of time and particularly in the case of processes in which the amount of acetylating medium employed is reduced to a minimum. 1

My invention, therefore, consistsin sub- 2 j ecting cellulose, preferably air dried to contain about 6 to 7%. of residual moisture,

such as may advantageously be prepared in the form of paper produced from pure cotton ina paper-making machine, to an-a'cetylating process by treatment with aceticanhydride, acetic. acid and a condensing agent such as sulphuric acid, and witha metallic catalyst consisting of. a salt of chromium. The product of acetylation is soluble in acetone without the necessity for any further treatment with water or dilute acid.

By metallic catalyst, I mean a salt of chromium which is operative even when added in a very small quantity relatively to chromium acetate are added this mixture .and then 2.5 lbs. of cellulose are introduced,

and thoroughly mixed for the necessary time.

As the acetylation process proceeds, the temperature is kept below about C. until a transparent viscous li uid free from fibres 1s obta1ne' d, and the mixing is stopped. The mixture 1s then maintained ata temperature of about C. until a test sample shows that the 'cellulose acetate is freely soluble in-acetone. This stage is reached very rapidly, the whole operation only requiring' about 18 hours from start to finish. The rate of the firststageof the acetv lation can be controlled and retarded if necessary by the partial neutralization of the sulphuric acidpresent by means of 0c-" casional additions of sodium carbonate.

These additions modify they beat evolutions of the reaction and so regulate its progress. I have fiound by experiment that the catalyst-may be added either in one addition and may consist of a single metallic salt, or

that the admixture of thejcatalyst may take place in two or more stages.

The catalyst maybe introduced into the solution by admixture therewith in the man ner above described, or in the metallic form, when it. will gradually pass 'into' solution in the acetylating mixture.

Having now particularly described and ascertained the nature of my said invention, and in what manner the same is to be per formed, I declare that what I claim'is:- 1. A process for the production of cellulose acetate consisting in treating cellulose with a mixture of acetic acid, acetic anhydrlde' and a condensing agent, and a metallic catalyst, consisting of a salt of chromium.

"2. A process as claimed in claim 1, where in the catalyst is added to the solution in stages. I 3. A process as claimed in claim 1, where in the. catalyst is added in the metallic form' and passes into solution during the process of acetylation.

LEoNARnAN'eELo rm. 

